For the purposes of this application the terms absorption and absorbent will include both absorption and adsorption processes.
It is a well established technique to remove CO.sub.2 from expiration gases during anesthesia by means of absorption using mixtures of hydroxides, such as soda lime (a commonly accepted designation of a mixture of sodium and calcium hydroxide). The soda lime is placed in a canister, and expiration gases are passed through the canister, whereby the CO.sub.2 reacts to form carbonates, and thus is removed from the expired air. The reason for wanting to remove CO.sub.2 is that the anesthetic gases used are expensive and it is desirable to reuse the portion not consumed by the patient. The use of hydroxides has been in practice for more than 80 years since D. E. Jackson designed the first machine to be used in a closed system for anesthesia, and numerous improvements have been described in the literature and patents since then.
It should be noted that the processes occurring in this type of devices are in principle irreversible chemical reactions, where the CO.sub.2 and the hydroxides react and carbonates are formed. These carbonates are not easily regenerated such that the hydroxides may be recovered.